It is quite common to administer a predetermined dosage of a drug to a patient over time by first diluting the drug in a liquid vehicle such as saline. Generally, the drug is mixed with the liquid vehicle, and the resulting solution is then administered intravenously to the patient. However, such systems require that the drug be carefully mixed into the solution for proper delivery.
To simplify the administration and storage of certain drugs, they are provided in a crystal form. The crystals are then mixed with a physiologically tolerable solution until the crystals dissolve. Unfortunately, unless care is taken to be sure the crystals are completely dissolved before the mixture is administered to the patient, adverse effects can result.
Various proposals have been made over time to mix a drug into a solution such as saline before it is administered to the patient. One such device is the CRIS system sold by IVAC of San Diego, Calif. In that system, the saline infuses into a container holding the drug solution. The mixture of the saline and drug is then delivered to the patient. Unfortunately, while the CRIS system allows diluted drug to be administered, it provides the drug at a changing dilution over time. As the system operates, the dilution of the drug increases as more and more drug is "washed out" of the container.
Other devices have been proposed which allow the drug to leach through a membrane to be delivered into a stream of saline over time. Unfortunately, there is no control over the leaching process and the dilution of the drug decreases over time. In addition, should the flow of saline be stopped, the drug will continue to leach into the saline. If the flow is then restarted, a concentrated and possibly dangerous flow of saline and drug will be delivered to the patient.
Accordingly what is needed is a system which provides a relatively constant dilution of drug to the patient. Such a system should provide a barrier against possible infusion of crystals from the preparation of the drug or possible bacteria which may be accidentally introduced into the drug solution. In addition, such a system should inherently prevent an excess of concentration of drug from being delivered to the patient. The self-regulated therapeutic agent delivery system, apparatus and method of the present invention meets these desires.